How I Use the Magnehelic.

As I wrote in the previous post, a magnehelic is an excellent way to get a sense of the valve status and think about how long they might have left before needing restoration. However, the magnehelic machine is even more valuable as a quality control tool. Some other useful things that I use the machine to check are...

Joint Seal

Full joint saturation is critical and there are places on the horn where a visual inspection of the joint isn’t possible. An alternate method to check for leaks is to stop up one end of the horn, submerge it in water, and then blow into the other end. Any leaks will reveal themselves as bubbles rising from the spot of the leak. This presents problems though because after the test, the joint is full of water. Since solder melts at a higher temperature than water, it turns to steam. Trying to add or resolder a wet joint will often cause solder to violently erupt from the joint. By using the magnehelic to find any joints that may not have properly sealed, it ensures that even if I make a mistake (unlikely but possible) it can be confidently fixed and doesn’t make it out the door. The magnehelic is also more sensitive than the bubble test and can find smaller gaps and holes.

Valve Machine Tolerances

I use brand new valve sections exclusively in my work. You won’t find a new Medlin Signature horn with a rebuilt valve machine. This means that I generally don’t have to worry about valves failing, but I do have to be a final quality control point for the fabrication of the valves. Really good machining produces very tight tolerances and the numbers I get from the magnehelic are effectively zero. However, I have had a few sloppy valve machines that required attention before going into a horn. I also keep track of the manufacturing precision over time so that I can monitor any long term trends. Without the magnehelic, it is unlikely that I would be able to check this.

Water key seal

Much like a woodwind tech worries about pad seal, I also check water key seal. On lever style keys, improper fit can be visually hidden, but not from the magnehelic. On Amado keys, it’s important to keep data on the seal inside the piston to know when to replace it.

Slide tube tolerance

On a brand new section of slide tube, I like to keep track of how tight the inner and outer tube is in relation to each other. To do this, I check the compression of the tube and see how much of the inner slide must be inserted into the outer slide to create a perfect seal. This is done dry, without lubrication, and the tube making tooling is adjusted if necessary to hit the ¼ inch mark.

By finding objective ways of measuring and keeping track of horn quality markers, it’s easy to track the development process and make even more ambitious goals. It’s frustrating for both players and makers when the evaluation of a horn is done entirely subjectively, especially if the maker and player have different philosophies of sound and technique. Some objective measurements give the player and maker a starting point to agree that the horn meets a high standard, before tackling the individual fit to each player. The magnehelic machine plays a major part in providing consistent data points.